block: xen-blkback: use API provided by xenbus module to map rings

The xenbus module provides xenbus_map_ring_valloc() and
xenbus_map_ring_vfree().  Use these to map the ring pages granted by
the frontend.

Acked-by: Jens Axboe <[email protected]>
Signed-off-by: David Vrabel <[email protected]>
Signed-off-by: Konrad Rzeszutek Wilk <[email protected]>
2 files changed